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Automatic Trans.

difference between early & later 727

I've been looking for a rebuilt kit for my small block 727. Seems everyone differentiates between 70 and earlier and 71 and later. Anyone know what the difference is? Or how I can tell which I have?

1970 & earlier:

- narrow bushing high clutch drum with 2 oil ports 180 apart.

- Flat snap ring used in high clutch drum

- corresponding narrow bushing journal on front pump reaction shaft support and large oil port for high clutch piston.

- Solid kickdown servo piston with 1 or 2 springs

- Different piston lip seal dimension wide vs. short lip

- 1966 & earlier had 19 spline input shaft

- 1966 & earlier had 10 spring peg high clutch piston.


- Wide bushing high clutch drum with 1 slotted oil port.

- corresponding wider bushing journal on pump reaction shaft support and smaller oil port for high clutch application.

- Controlled load kickdown servo piston with oil cushioned inner piston with only 1 spring

- Flex bands introduced

- Wavy snap ring in high clutch drum

- 1967+ had 24 spline input shaft

- 1976+ had 37.5 pressure angle on front planetary for improved strength

- Part throttle kickdown valve added

- Lock-up converters 1978+

- Smaller orifices in VB to feed servos with less harsh shifts

- 15 spring peg high clutch piston

Many more differences......

If you look at the driver's side of the trans just above the oil pan rail between the front cooler line & neutral safety switch, you will see a machined pad with stamped numbers. Decode number with below link to find year and application.


I`ve been looking for a rebuildable big block 727 core. Which years trans would be the strongest offered from the factory? Are any of the 68-69-70 HP cores the same internally. What makes them a HP.? Should I be seeking a 1971-74 core or should I stick with the 68-70 vintage?

badgtx - I would say '68-'70 are good ones. HP models had a 4 clutch 3rd gear drum & 4 pinion planetaries. Also, '68-'70 had the better kickdown servo (solid with 2 return springs). The '71+ has the better high clutch drum with the wider bushing to support the drum better, and help prevent sealing ring wear. So, you could use a couple of tranmissions to come up with the best set-up. Use a '68-'70 core with 4 pinion planetaries, solid kickdown servo with 2 springs, and the '71+ 4 clutch drum/front pump. Use a red lined solid band with 3.8 or 4.2 lever. John


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